1. Field of the Invention
The present general inventive concept relates to a hard disk drive, and more particularly, to a hard disk drive which can effectively prevent generation of sticking so that a disk can smoothly rotate. Thus, the performance and reliability of the hard disk drive are improved.
2. Description of the Related Art
Hard disk drives (HDDs) formed of electronic parts and mechanical parts is are memory devices to record and reproduce data by converting digital electric pulses to a magnetic field that is more permanent. The HDDs are widely used as auxiliary memory devices of computer systems because they are capable of providing fast access time to a large amount of data.
With the recent increase in TPI (track per inch; a density in a direction along a radius of a disk) and BPI (bits per inch; a density in a direction along a thickness of a disk), and because BPI×TPI=BPSI, the HDD has achieved high areal density capacities and its field of application has expanded. Areal density, also sometimes called bit density, refers to the amount of data that can be stored in a given amount of area on a hard disk recording medium. Since disk surfaces are of course two-dimensional, areal density is a measure of a number of bits that can be stored in a unit of area. It is usually expressed in bits per square inch (BPSI). The general structure of the HDD will be briefly described with reference to FIGS. 1 through 3.
FIG. 1 is a partial cross-section view of a conventional HDD. FIG. 2 is an enlarged view of a portion A of FIG. 1. FIG. 3 is a view illustrating a state in which a fluid dynamic bearing (FDB) is stuck to an FDB fixing portion of FIG. 2 by an external force. As illustrated in FIGS. 1, 2, and 3, a conventional HDD includes a disk 110 coated with a magnetic material for recording and storing data, a spindle motor 140 on which the disk 110 is supported and which is capable of rotating, and a base 130 on which the disk 110 and the spindle motor 140 are assembled. The other elements will be described below.
The spindle motor 140 includes a fluid dynamic bearing (FDB) 150, a hub 160 partially coupled to the FDB 150 and supporting the disk 110, and a power generation portion 170 generating power to rotate the hub 160. The FDB 150 includes an FDB fixing portion 151 fixed to the base 130 by a flange 144 located thereunder and an FDB rotation portion 153 partially inserted in the FDB fixing portion 151 and relatively rotating with relative respect to the FDB fixing portion 151, to form a rotation center of and with the hub 160.
An insertion groove portion 151a in which the FDB rotation portion 153 is inserted is formed in the FDB fixing portion 151. The insertion groove portion 151a is filled with a predetermined fluid 152. The fluid 152 performs a role of not only supporting a weight of the hub 160, the disk 110, and the spacer 113 coupled to the FDB rotation portion 153 but also of allowing the FDB rotation portion 153 to freely rotate in the insertion groove portion 151a. 
The FDB rotation portion 153 includes a rotation shaft portion 154 formed lengthwise in a vertical direction and coupled to the hub 160 in an upper area and a shaft support portion 155 formed in a lower portion of the rotation shaft portion 154 to be relatively larger compared to a cross sectional area of the rotation shaft portion 154. A plurality of fluid groove portions 156a and 156b are formed in an outer surface of the rotation shaft portion 154 and the shaft support portion 155, respectively. As the fluid 152 filling an inside of the insertion groove portion 151a freely flows in the fluid groove portions 156a and 156b, the FDB rotation portion 153 smoothly rotates.
In the meantime, the disk 110 and the hub 160 vibrate for various reasons, for example, when an impact stronger than a load of a hydraulic pressure provided by the fluid 152 is applied to the spindle motor 140. Accordingly, a position of the FDB rotation portion 153 is moved so that the FDB rotation portion 153 strongly collides against an inner wall of the FDB fixing portion 151 in the insertion groove portion 151a. In this case, the fluid groove portion 156a is blocked so that the fluid 152 cannot flow freely. Consequently, the FDB rotation portion 153 is stuck to the inner wall of the FDB fixing portion 151 (please refer to a portion P of FIG. 3). Thus, a sticking phenomenon may occur where the rotation of the FDB rotation portion 153 is restricted.
When the rotation of the FDB rotation portion 153 is restricted, the hub 160 coupled to the FDB rotation portion 153 does not rotate and thus the disk 110 coupled to the hub 160 does not rotate. However, in the conventional HDD, since no mechanical portion to prevent the sticking phenomenon is provided, smooth rotation of the disk 110 is not guaranteed so that the performance and reliability of the HDD are deteriorated.